(a) Field of the Invention
The present invention is related to a system for indicating a broadcasting station frequency received by a superheterodyne radio receiver.
(b) Description of the Prior Art
Some radio receivers incorporate a system for electrically detecting and indicating frequency of a station signal received.
Known station-signal frequency indicating system mentioned above usually is designed so that a signal generated at a local oscillator in the receiver is repetitively counted by a frequency counter which is preset at a fixed number corresponding to an intermediate frequency to which is tuned an IF-amplifier stage of the receiver. The content in this frequency counter at the end of each counting period is displayed on a digital or analog indicator, which represents the local oscillating frequency plus or minus the preset number (Intermediate Frequency). Actually, such an arrangement can give a correct indication of the received station-signal frequency, provided that the receiver is tuned exactly to the station. However, when the receiver is only slightly detuned from the broadcast signal frequency, it is no longer capable of indicating the station-signal frequency, but displays a tuning frequency of the receiver itself, in spite of the same station signal being uninterruptedly received.